This disclosure relates to a modular control apparatus, particularly a safety switching apparatus. The modular control apparatus has a head module, at least one supply module and at least one peripheral module, which are arranged next to one another on the head module.
The disclosure additionally relates to a supply module for such a control apparatus.
The applicant markets modular control apparatuses of the above-mentioned type under the name of PSS Universal, as described in the system description, No. 21256-EN-04 from the applicant.
A control apparatus can be for instance a modular control apparatus for a configurable or programmable controller. A control apparatus is made up in modular fashion from a central head unit and modules arranged next to one another. The modules are connected to one another and to the head module via a separate bus. The modules are predominantly input and output modules that can be used to connect the peripherals to be controlled. Therefore, the input and output modules are often also referred to as peripheral modules. Input modules pick up signals from the external peripherals, for example signaling devices such as door contact switches, light barriers or emergency off switches. The output modules are used to control, and if need be supply current to, connected actuators, for example contactors, solenoid valves and lamps. The current required for this purpose is provided for the output modules via the supply modules.
The supply modules, like input and output modules, are arranged on the control apparatus and connected to the shared bus. External connections on the supply modules can be used to supply a peripheral current to the control apparatus, and the bus can be used to forward said peripheral current to the appropriate output modules. The peripheral current is provided by external power supply units, which convert a mains voltage of 230 volts AC into a corresponding operating voltage of 24 volts DC, for example. The power supply units are designed to provide different current levels and have protected mechanisms, for example in the form of fuses, that trip and interrupt the current path to the control unit when a certain threshold value is exceeded.
Usually, multiple output modules are supplied with current by a single supply module, as is also described in the system description of the PSS Universal No. 21256-EN-04 cited at the outset. In addition, within a control apparatus, different potential groups are formed that are each made up of a supply module and associated output modules. The modules of one potential group are arranged contiguously on the bus, each potential group beginning with a supply module. The more output modules are associated with a single supply module, the higher, usually, the current that a supply module picks up externally.
Particularly in the case of power peaks, for example when switching on and off, the load can become too high for a supply module, so that either an internal fuse or an external fuse of the external power supply unit trips and isolates the control apparatus and/or individual potential groups. This can fundamentally prevent the control apparatus or individual modules from becoming damaged. Uncontrolled disconnection of this kind is undesirable, however, and has an adverse effect on the availability of the overall system.